CNC bore slotting machining system

ABSTRACT

A bore slotting machine for cutting radially spaced longitudinal slots in sleeves for automotive power steering units comprising a cutting face adapted to operate with a bore of a component being worked; a motorized drive adapted to impart reciprocating motion to the cutting face; a positional feedback device associated with the cutting face and adapted to communicate with a computer; a chuck adapted to hold a component being worked at a location adjacent the cutting face and being supported for indexible rotational movement about a Y axis substantially parallel to that of the bore in the component being worked; a first shuttle carriage carrying the workholding device such shuttle being adapted for linear motion perpendicular to the bore axis of the component under the influence of a first servo drive; a second shuttle carriage adapted to carry the cutting face and associated motorized drive such that movement of the second carriage achieves linear reversible relative motion between the component being worked and the cutting face along an axis parallel to the bore axis; a second servo drive for actuating the second shuttle carriage; a controlling computer for activating the cutting face drive and synchronizing the first and second servo drives with the position of the cutting face; each drive having a closed loop control system incorporating a feedback device.

The present invention relates to bore slotting machinery and inparticular to apparatus of the type utilising a reciprocating cuttingface to produce one or more longitudinal slots in the bore of acomponent.

For many year various apparatus have been proposed for cuttinglongitudinal slots in the bores of relatively small sleeves such asthose utilised in automotive rotary power steering valves. The design ofsuch machinery necessarily involves relative movement between thecutting face and the component being worked along and about multipleaxes; precision synchronisation of the high speed movements relative tothe various axes being of critical importance. In addition to thesynchronised movements required to achieve the actual cut the cuttingface of the tool and/or the workholding member must be capable ofmovement to facilitate loading and unloading of the workholding memberwithout interference with the cutting face.

To date a number of mechanical arrangement have been proposed in orderto achieve the high speed synchronised relative movement between aworkholding member and the cutting face necessary for the cuttingoperation and also to facilitate relative displacement of the componentfor loading and unloading during both the cutting and loading/unloadingoperations.

It is the object of the present invention to provide an alternate boreslotting machine which utilises computer controlled servo drives tocontrol and synchronise at least some of the relative motions betweenthe cutting face and the workholding member. The term "servo drive"where used throughout this specification is intended to encompass anytype of servo driven motor or actuator including conventional motors,servo motors, linear motors, hydraulic activators, pneumatic linearactuators and rotary actuators.

The use of a servo drive system as opposed to mechanical configurationsto control bore slotting machinery is particularly advantageous as ithas been found that comparable speeds may be obtained to those achievedby mechanically synchronised equipment whereas electronicallysynchronised equipment eliminates the need for complicated mechanicallinkages and is not subject to the wear rates and associated frequentservice requirements of mechanically synchronised equipment.

Electronically synchronised bore slotting machinery is furthermorebetter adapted for situations where components of different dimensionsare to be produced having regard to the fact that the CNC parameters maybe programmed, stored and recalled far more quickly than replacement,adjustment and/or alteration of mechanical components of comprising thesystem.

In addition, greater accuracy of the position, size and surface finishof the generated slots may be achieved because of the mechanicalsimplicity of the servo controlled machinery, and the ability to usefeedback to compensate for variation and imperfections in the machineelements.

According to the present invention there is provided a bore slottingmachine comprising a cutting face adapted to operate within a bore of acomponent being worked; a motorised drive adapted to impartreciprocating motion to the cutting face; an electronic positionalfeedback device associated with the cutting face; a workholding deviceadapted to hold a component being worked at a location adjacent thecutting arm and being supported for indexible rotational movement aboutan axis substantially parallel to that of the bore in the componentbeing worked; a first shuttle being adapted for linear movement along anaxis parallel to the bore axis and a second shuttle carrying either theworkholding device or the cutting face, the second shuttle being adaptedfor linear motion perpendicular to the bore axis of the component underthe control of a servo drive; the first shuttle carriage adapted tocarry parts of the machine such that movement of the carriage achieveslinear reversible relative motion between the component being worked andthe cutting face parallel to the bore axis; a servo drive for actuatingthe first shuttle carriage; computer control means for activating thetwo servo drives and synchronising the two drives; each drive having aclosed loop computer control system incorporating a feedback device.

One embodiment of the present invention will now be described withreference to the accompanying drawings in which:

FIG. 1 is a perspective view of a machine in accordance with the presentinvention;

FIG. 2 is an exploded perspective view of part of the machine of FIG. 1.

The embodiment of FIG. 1 depicts a CNC machining system having a base 1with an upstanding column 2 extending thereabove. Upstanding column 2 isprovided with guide rails 3 adapted to constrain a first shuttlecarriage 4 for a range of reversible vertical movement under theinfluence of drive shaft 5 operated by linear electric servo drive 6.

Electric servo drive 7 is mounted to shuttle carriage 4 via anappropriate translatory crank mechanism (not shown) adapted to impartoscillatory reversing rotational movement to spindle 8 and angularreciprocating motion to cutting arm 9 and cutting face 10.

As may best be viewed from FIG. 2 the sleeve 11 being worked is held inchuck 12 mounted in turn to spindle 13. Spindle 13 is mounted on asecond shuttle carriage 14 and is capable of being rotated about a "Y"axis by servo drive 15 and intermediate worm drive 16. Closed loopcontrol of servo drive 15 is facilitated by feedback device 17 being arotary encoder. Shuttle carriage 14, servo drive 15, chuck 12 and hencethe sleeve 11 being worked are all supported for reversible lineartravel along axis X by rails 18 under the influence of electric servodrive motor 19 and ball screw drive shaft 20.

It will be appreciated that the reciprocating arcuate travel of cuttingarm 9 imparts reciprocating arcuate travel to cutting face 10. In orderthat this arcuate travel of cutting face 10 is capable of cutting slotsaligned with axis Y' in the bore sleeve 11 a fast reciprocating motionmust be imparted to shuttle carriage 14 in order to maintain full reliefof the cutting head 10 from the work face in the bore of sleeve 11during the return stroke of the cutting arm as opposed to the cuttingstroke. For each cutting stroke the cutting head must be advanced to anew position and held stationary for the full duration of engagement ofthe cutting face in the bore. This reciprocating motion of shuttlecarriage 14 must be synchronised with the oscillating arcuate movementof cutting face 10 to maintain the correct relative position profile andhence there is common computer control (not shown) of the two drives.The control of these servo drives is also of a closed loop nature suchthat feedback devices constantly input to the controlling computer theposition of the components controlled by the respective drives.

Drive 19 is also responsible for moving chuck 12 and hence sleeve 11from the working position depicted in unbroken lines in FIG. 1 to theloading and unloading position depicted in broken lines at 21 in FIG. 1.

It will furthermore be appreciated that servo drive 19 by way of itscontrol of shuttle 14 is also responsible for controlling the depth ofcut for the slot (not shown) being formed by cutting face 10 in the boreof sleeve 11 and hence drive 19 is responsible for advancing sleeve 11onto cutting face 10 during the cutting operation.

It will also be appreciated that the first shuttle carriage 4 may carrythe sleeve 11 and second shuttle carriage 14 may carry the cutting face10, such that the sleeve 11 is moved parallel to the Y axis and thecutting face 10 is moved along the X axis. In this embodiment, the servodrives 6 and 19 are controllable to effect the same motion of thecutting face relative to the sleeve as in the previous embodiment,however, since the sleeve is above the cutting face 10, the bottom ofthe sleeve 11 would be cut by the cutting face 10.

Electric servo drive motor 15 is responsible for determining the radialposition of the slot (not shown) being cut by cutting face 10 in sleeve11 as it controls via worm drive 16 and chuck 12 rotation of sleeve 11relative to cutting face 10. Once again this motion must be synchronisedwith that of servo drives 7 and 19. Synchronisation is best achieved byway of common computer control and closed loop control of each drivefacilitated by feedback devices (only one shown at 17). Typically anumber of radially separated slots parallel with axis Y' would be cut insleeve 11 and drive 15 would control the radial separation of the slots.

The rotation of chuck 12 by electric servo drive motor 15 not onlydetermines the radial displacement of one slot from an adjacent slot butalso achieves compensation for any lack of concentricity in the sleeveidentified during a probing operation performed by the machine prior tothe cutting operation.

The aforementioned probing operation will now be described hereafter.The probing operation will be familiar to any person skilled in the artof machining circular objects which need to have controlled runout inorder that the finished product may fall within acceptable concentricityranges.

A sleeve being worked is loaded onto an input conveyor with its axis ina vertical orientation. The input conveyor then carries the sleeve to aloading station where the sleeve is transferred from the conveyor to apick-up nest. A four position indexing unit fitted with gripper armslowers, grips the sleeve, raises, then indexes ninety degrees to theprobe station 22 where it lowers, releases the sleeve, then raises awayfrom the probe station.

At the probe station the sleeve is clamped within a collet. The colletis then rotated, via a toothed belt drive, until the hitch pin hole islocated and positioned via a photo-electric cell. The sleeve is thenmaintained in this orientation for probing before loading into themachining station. After orientation, the probe unit lowers and measuresthe runout of the sleeve bore relative to the O.D. of the sleeve and thehitch pin hole position. This data is then stored in the controlcomputer for later use in cutting position competisation during themachining operation.

It will be appreciated that once the concentricity information has beenobtained with respect to a particular component in the conventionalmanner above described the information may readily be incorporated intothe programming of the control computer such that chuck 15 may berotated prior to the cutting operation so as to ensure that all slotswhich are cut are radially aligned with the centre of the bore of thecomponent as compared with the actual centre of the clamping axis. Theclamping axis is related to the external surface of a component as wellas the axis about which the chuck rotates. Compensation in this mannermay result in slots on one side of the sleeve being slightly deeper thanslots on the other side of the sleeve although this is of littleconsequence in relation to many components which are manufactured by thesubject machinery and in particular power steering sleeves forautomobiles. It is more important that the radial disposition of theslots is true to the internal bore dimensions of the component ratherthan to have slots of precisely the same depth.

Electric servo drive motor 6 is responsible for removing cutting face 10from sleeve 11 to facilitate loading of fresh sleeves to be worked andunloading of worked sleeves. In the case of some longer slots it is alsonecessary to move first shuttle carriage 4 as the cutting of eachindividual slot progresses in order that the cutting face may beimparted with adequate reach for the desired length of slot. It istherefore desirable that drive 6 is similarly linked to a commoncomputerized control unit (not shown) to that controlling drives 15, 19and 7 in order that the cutting action may proceed in each sleeve andfrom sleeve to sleeve. Once again closed loop computer control isutilised with a feedback device (not shown) imparting control over theprecise position of the cutting face at any time.

The applicant has found that the Siemens Sinumerik 840 C TM range of CNCcontrollers are appropriate for controlling the electronic servo drivesutilised in the abovementioned embodiment and that, rather thanconventional CNC programming, interpolation and compensation with tablesis utilised with the spindle axis as the master axis and the remainingdrives configured as slave axes. In this manner the table ofrelationships between slave function positions and master functionpositions may be loaded into the computers memory prior to the runningof the programmed cycle as opposed to such information beingprogressively loaded during the cycle as is the case in normal CNCprogramming. Far superior processing speed is thereby achieved. Blockcycle times of 4.0 milliseconds have been utilised with interpolationclock cycles of 4.0 milliseconds, position control cycles of 1.0millisecond and drive basic cycle times of 0.5 milliseconds.

For simplicity FIG. 1 does not include detail of ancillary equipmentnecessary for operation of bore slotting machinery such as apparatus forloading and unloading sleeves from the chuck and for removing cuttingmaterial.

We claim:
 1. A bore slotting machine comprising:a cutting faceinsertable within a bore of a component being worked; a motorized drivefor imparting reciprocating motion to the cutting face; a positionalfeedback device associated with the cutting face and in communicationwith a computer; a workholding device for holding a component beingworked at a location adjacent the cutting face and being supported forindexible rotational movement about a Y' axis substantially parallel tothat of the bore in the component being worked; a first shuttle carriageand a second shuttle carriage; the second shuttle carriage carrying oneof the workholding device and the cutting face, the second shuttlecarriage being displaceable for linear motion substantiallyperpendicular to the Y' axis; the first shuttle carriage for carryingpart of the machine such that movement of the first shuttle carriageachieves linear reversible relative motion between the component beingworked and the cutting face along an axis substantially parallel to theY' axis; a first servo drive for actuating the first shuttle carriage; asecond servo drive for actuating the second shuttle carriage; and acomputer for controlling the cutting face drive and synchronizing thefirst and second servo drives with the position of the cutting face. 2.A bore slotting machine in accordance with claim 1, wherein each drivehas a closed loop control system incorporating a feedback device.
 3. Abore slotting machine in accordance with claim 1, wherein thereciprocating motion of the cutting face is angular reciprocating motionabout an axis perpendicular to the bore of the component being worked.4. A bore slotting machine in accordance with claim 1, wherein thereciprocating motion of the cutting face is linear reciprocating motionalong an axis parallel to that of the bore of the component beingworked.
 5. A bore slotting machine in accordance with claim 1, whereinthe second shuttle carriage carries the workholding device and the firstshuttle carriage carries the cutting face and associated motorizeddrive.
 6. A bore slotting machine in accordance with claim 1, whereinthe indexible rotational movement of the workholding device about theY'axis is imparted by a third servo drive under the control of thecomputer and synchronized to at least the cutting face drive.
 7. A boreslotting machine in accordance with claim 1, wherein the computercontrols the servo drives using a program utilizing the cutting drive asa master drive and the remaining drives as slave drives.
 8. A boreslotting machine in accordance with claim 1, wherein the computercontrol for the servo drives provides interpolation and compensationusing tables with the cutting face drive as a master drive and theremaining drives as slave drives.
 9. A bore slotting machine inaccordance with claim 1, wherein the first servo drive comprises alinear electronic motor drive.
 10. A bore slotting machine in accordancewith claim 1, wherein the second servo drive comprises a linear motor.11. A bore slotting machine in accordance with claim 1, furthercomprising:a runout measuring probe for determining runout informationbased on differences between an external clamping diameter of thecomponent being worked and an internal bore diameter of the component;means for transferring the runout information to the computer; means foradjusting rotational movement of the workholding device based on therunout information to ensure that radial disposition of slots being cutin the bore is referenced to the center of the bore of the componentrather than a center of the external clamped diameter of the component.